I would dare to say that it depends on the venue.
While the effect itself gets killer reactions, with the correct patter and presentation you can juice all there it is from the effect.
If you are performing at someone's home for instance, I agree with casey that the clock is a great way to reveal it. If you are a working magician in venues like a restaurant or coffe shop, use your enviroment. For instance, try to appear it on the salt shaker. Or inside a sugar packet that has been in the table the whole time.
I think that it is also important that you chose locations that are really "Impossible". For example, if you appear it on the card box, some people may think the cardbox is gimmicked or something, or if you appear it on the spectator pocket they may think you somehow you managed to put it there.
but stabbed in the clock? or inside a sealed sugar packet? or a salt shaker? Now that in my opinion just astounds them.